Author here. Quick sidenote: this is chapter 2 of a book aiming at teaching the terminal and related tooling (make, jq, regular expressions, etc) to beginners and people trying to become developers.
I've been on the job for 10 years and I still use these tools daily. For example, I sent a PR yesterday that was adding a configuration entry on 150+ config files by using find, grep and sed.
I'm not pretending these are the only tools that exist, but darn are they handy sometimes, and good to have in your toolbelt.